1. Field of the Invention
This invention relates to devices for sensing selected conditions in confined areas and/or in combination with moving parts and, more particularly, to devices for sensing the temperature of and/or pressure at moving parts in confined or enclosed areas and providing a remote reading of the sensed condition.
2. Description of the Prior Art
This invention will be described as embodied in apparatus for monitoring temperatures and pressures in an automatic transmission. It will be appreciated that a number of other applications are possible, for example to measure strain or vibration in a member, the temperature of a piston, the pressure behind the rings in a piston in an internal combustion engine, or pressure and temperature at gas turbine blades.
There are a number of available technologies for achieving those objectives, but a major problem is to get the sensed condition out of the enclosed areas as a reliable, usable signal, and in a cost effective manner. For example, it has been proposed to bring signals out of an engine using slip rings, and/or mechanical linkages. These have a number of inherent problems. Slip rings are susceptible to electrical noise which affects reliability. Mechanical linkages are difficult to install, requiring extensive modifications to the engine, and are limited as to the speeds to which they can be exposed, i.e., engine RPM.
Another previous method proposed for measuring the temperature of a piston in an internal combustion engine, for example, is to incorporate a plug in the piston wherever a temperature reading is required. These plugs are made of a specially treated alloy capable of withstanding elevated temperatures for a specific period of time. But certain characteristics of the plug, e.g., hardness, are affected by the elevated temperatures, and changes in those characteristics are used to arrive at temperature measurement.
An example of this type of measurement system is disclosed in U.S. Pat. No. 4,787,242 issued Nov. 29, 1988 to Shine. In this patent, an Aluminum-Copper alloy plug is incorporated into the piston. This plug can be a band integrally cast with the piston, a setscrew, or a wedge that is press-fit into the piston. This plug is subjected to a qualifying run of at least 100 hours and the hardness of the plug is then measured. The steady-state temperature of the piston is then calculated by reference to a calibration curve graphing hardness verses temperature for the given alloy mixture. A problem with this type of piston measuring device is that it will not respond to fast temperature transients on the surface of the piston. Further, these devices must be removed from the piston, sent to a laboratory to be tested for hardness, and then the temperature of the piston calculated from the calibration curve. This is a very time consuming process and is unacceptable where the temperature of the piston is needed immediately.
An effective solution to some of these problems is disclosed and claimed in U.S. Pat. No. 5,106,202, assigned to the assignee of this application. That patent uses infrared technology and is quite effective, but has one drawback in that it is limited to line of sight applications.
Devices of the type to which this invention relates will find important application as a research tool in selecting materials and formulating fuel and lubrication products, and also in road testing vehicle components such as an automatic transmission.